NAME

REINDEX - rebuild indexes

SYNOPSIS

REINDEX { INDEX | TABLE | DATABASE | SYSTEM } name [ FORCE ]

DESCRIPTION

REINDEX rebuilds an index using the data stored in the index’s table,
replacing the old copy of the index. There are several scenarios in
which to use REINDEX:
· An index has become corrupted, and no longer contains valid data.
Although in theory this should never happen, in practice indexes can
become corrupted due to software bugs or hardware failures. REINDEX
provides a recovery method.
· An index has become ‘‘bloated’’, that it is contains many empty or
nearly-empty pages. This can occur with B-tree indexes in PostgreSQL
under certain uncommon access patterns. REINDEX provides a way to
reduce the space consumption of the index by writing a new version of
the index without the dead pages. See in the documentation for more
information.
· You have altered a storage parameter (such as fillfactor) for an
index, and wish to ensure that the change has taken full effect.
· An index build with the CONCURRENTLY option failed, leaving an
‘‘invalid’’ index. Such indexes are useless but it can be convenient
to use REINDEX to rebuild them. Note that REINDEX will not perform a
concurrent build. To build the index without interfering with
production you should drop the index and reissue the CREATEINDEXCONCURRENTLY command.

PARAMETERS

INDEX Recreate the specified index.
TABLE Recreate all indexes of the specified table. If the table has a
secondary ‘‘TOAST’’ table, that is reindexed as well.
DATABASE
Recreate all indexes within the current database. Indexes on
shared system catalogs are skipped except in stand-alone mode
(see below). This form of REINDEX cannot be executed inside a
transaction block.
SYSTEM Recreate all indexes on system catalogs within the current
database. Indexes on user tables are not processed. Also,
indexes on shared system catalogs are skipped except in stand-
alone mode (see below). This form of REINDEX cannot be executed
inside a transaction block.
name The name of the specific index, table, or database to be
reindexed. Index and table names can be schema-qualified.
Presently, REINDEXDATABASE and REINDEXSYSTEM can only reindex
the current database, so their parameter must match the current
database’s name.
FORCE This is an obsolete option; it is ignored if specified.

NOTES

If you suspect corruption of an index on a user table, you can simply
rebuild that index, or all indexes on the table, using REINDEXINDEX or
REINDEXTABLE.
Things are more difficult if you need to recover from corruption of an
index on a system table. In this case it’s important for the system to
not have used any of the suspect indexes itself. (Indeed, in this sort
of scenario you might find that server processes are crashing
immediately at start-up, due to reliance on the corrupted indexes.) To
recover safely, the server must be started with the -P option, which
prevents it from using indexes for system catalog lookups.
One way to do this is to shut down the server and start a single-user
PostgreSQL server with the -P option included on its command line.
Then, REINDEXDATABASE, REINDEXSYSTEM, REINDEXTABLE, or REINDEXINDEX
can be issued, depending on how much you want to reconstruct. If in
doubt, use REINDEXSYSTEM to select reconstruction of all system
indexes in the database. Then quit the single-user server session and
restart the regular server. See the postgres(1) reference page for
more information about how to interact with the single-user server
interface.
Alternatively, a regular server session can be started with -P included
in its command line options. The method for doing this varies across
clients, but in all libpq-based clients, it is possible to set the
PGOPTIONS environment variable to -P before starting the client. Note
that while this method does not require locking out other clients, it
might still be wise to prevent other users from connecting to the
damaged database until repairs have been completed.
If corruption is suspected in the indexes of any of the shared system
catalogs (which are pg_authid, pg_auth_members, pg_database,
pg_pltemplate, pg_shdepend, pg_shdescription, and pg_tablespace), then
a standalone server must be used to repair it. REINDEX will not process
shared catalogs in multiuser mode.
For all indexes except the shared system catalogs, REINDEX is crash-
safe and transaction-safe. REINDEX is not crash-safe for shared
indexes, which is why this case is disallowed during normal operation.
If a failure occurs while reindexing one of these catalogs in
standalone mode, it will not be possible to restart the regular server
until the problem is rectified. (The typical symptom of a partially
rebuilt shared index is ‘‘index is not a btree’’ errors.)
REINDEX is similar to a drop and recreate of the index in that the
index contents are rebuilt from scratch. However, the locking
considerations are rather different. REINDEX locks out writes but not
reads of the index’s parent table. It also takes an exclusive lock on
the specific index being processed, which will block reads that attempt
to use that index. In contrast, DROPINDEX momentarily takes exclusive
lock on the parent table, blocking both writes and reads. The
subsequent CREATEINDEX locks out writes but not reads; since the index
is not there, no read will attempt to use it, meaning that there will
be no blocking but reads might be forced into expensive sequential
scans.
Reindexing a single index or table requires being the owner of that
index or table. Reindexing a database requires being the owner of the
database (note that the owner can therefore rebuild indexes of tables
owned by other users). Of course, superusers can always reindex
anything.
Prior to PostgreSQL 8.1, REINDEXDATABASE processed only system
indexes, not all indexes as one would expect from the name. This has
been changed to reduce the surprise factor. The old behavior is
available as REINDEXSYSTEM.
Prior to PostgreSQL 7.4, REINDEXTABLE did not automatically process
TOAST tables, and so those had to be reindexed by separate commands.
This is still possible, but redundant.

EXAMPLES

Rebuild a single index:
REINDEX INDEX my_index;
Rebuild all the indexes on the table my_table:
REINDEX TABLE my_table;
Rebuild all indexes in a particular database, without trusting the
system indexes to be valid already:
$ exportPGOPTIONS="-P"
$ psqlbroken_db
broken_db=> REINDEX DATABASE broken_db;
broken_db=> \q